1. Technical Field
The present invention relates to a Vertical-Cavity Surface-Emitting Laser diode (hereinafter referred to as VCSEL), an optical device, a light irradiation device, a data processing device, a light sending device, an optical spatial transmission device, an optical transmission system, and a method for manufacturing a VCSEL.
2. Related Art
In technical fields such as optical communication or optical storage, there has been a growing interest in VCSELs. VCSELs have excellent characteristics that edge-emitting semiconductor lasers do not have. For example, VCSELs are characterized by lower threshold current and smaller power consumption. With a VCSEL, a round light spot can be easily obtained. Also, evaluation can be performed while VCSELs are on a wafer, and light sources can be arranged in two-dimensional arrays. With these characteristics, demands especially as light sources in the communication and data storage fields have been expected to grow.
When a VCSEL is used as a light source in optical communication or optical storage, it is required that divergence angle or far field pattern (FFP) of laser light emitted from the VCSEL be smaller than a certain value. If divergence angle becomes greater, spot diameter becomes greater, thereby error occurrence in optical communication may increase, or resolution in reading or writing data from or to a storage media may be reduced.
In a GaAs-type VCSEL that emits 850-nm laser light, a high-Al-composition AlAs or AlGaAs is used for a current confining layer. The current confining layer is formed in a mesa, and oxidized to a certain distance from a side surface of the mesa in an oxidizing process to form a conductive region (oxidized aperture) inside surrounded by an oxidized region.
The divergence angle of a VCSEL depends on the diameter of an oxidized aperture formed in the current confining layer. More specifically, if the diameter of the oxidized aperture becomes smaller, divergence angle tends to become greater, and if the diameter of the oxidized aperture becomes greater, divergence angle tends to become smaller. In addition, the oxidized aperture is a critical factor in deciding lasing mode of laser light. In order to obtain a single-mode laser light, the oxidized aperture should be made smaller.
A mesa is processed in a cylindrical or rectangular shape by etching semiconductor layers stacked on a substrate. Depending on accuracy in the processing, the size of the diameter may vary. In addition, if a current confining layer is oxidized from a side surface of the mesa having such a structure, variations due to oxidation may also occur. Especially if the diameter of an oxidized aperture becomes as small as in single-mode, it is difficult to reproduce the diameter of the oxidized aperture, which makes it difficult to control divergence angle.
An object of the present invention is to provide a VCSEL in which divergence angle can be made smaller than that of related arts, and a module, a light source device, a data processing device, a light sending device, an optical spatial transmission device, and an optical spatial transmission system that use the VCSEL, and a method for manufacturing a VCSEL.